There are widely used razor blade units wherein one or two elongated razor blades, each with one cutting edge, are permanently secured in a housing made of molded plastic. Such blades are either provided with an integral handle (disposable units), or they are adapted to be attached to a handle by suitable coupling means. Such conventional blade units comprise a base member and a cap member, between which there are positioned one or two blades. When two blades are used, these are in a staggered position, with a spacer between them, with the cutting edges being offset, with a guard member in front of the cutting edge of the first blade, and another member behind the cutting edge of the second blade, both of which define the geometry of the shaving system, the plane defined by these and the position of the cutting edges respective this surface determining the shaving characteristics of the unit. This type of blades, with one or two blades, is very well known and such blades constitute a large percentage of the market of razor blades.
With conventional twin-blade razor blade units, the geometry of the blades and that of the two members of the housing, namely the guide in front of the blades (guard structure) and the member to the rear of the edges of the blades, defines a plane which determines the shaving characteristics.
The relation of the cutting edges of the blades vis-a-vis this plane is quite critical. According to the prior art, the exposure of the cutting edges is advantageously between -0.002 to +0,004 inch. The problem with prior art structures is in that the geometry is determined by the interaction of two parts made of molded plastic, which are machined to a high degree of accuracy, but which are secured with each other by a number of rivets (cold riveting), which rivets also serve as supports for the blades and spacer. The conventional blades are attached to a suitable handle by a rigid grip structure or by a swivel connection.
The critical blade edge parameters depend on the accuracy of the riveting of the two components of the housing, and this brings about certain variations from blade to blade unit.
Such conventional blade units comprise a base and a cap member, usually injection molded, intermediate of which are positioned one or two blades which are positioned on pins extending from the base member. When such a blade unit is assembled at the manufacturing plant, the blades with the interposition of a spacer between two blades are set on said pins which pass through holes in the blades and spacer, whereupon the cap member is also set on the pins, these latter are deformed at their outermost ends to constitute rivet heads, so fixedly uniting all parts and holding them together. As is well known, the blade or blades have to be accurately positioned in the unit relative to one another, with a minimum of tolerances being allowable. However, attaching the two members (cap and base) with one another and causing the above mentioned heading of the pins has also the consequence of displacing the individual blades and disturbing the relative position between them, as well as their position relative in the holding members.